1. Field of the Invention
The present invention relates in general to center pivot irrigation systems having swing arms for providing water to the comers of a field and more specifically relates to a guidance system that is utilized for controlling the travel of the swing arm on a desired path.
2. Description of the Prior Art
Center pivot irrigation systems have long been known in the art for providing water to large sections of land. A typical center pivot system is capable of irrigating one hundred and sixty acres or more. A center pivot system is formed of a main arm water conduit that is fixed at one end to a central point of water supply. The main arm is supported on a plurality of wheeled towers and is pivotally attached to the source of water to provide a circular irrigation pattern surrounding such supply.
Center pivot irrigation systems have proven to be highly efficient in irrigating large sections of land. They suffer from the deficiency that they produce a circular water pattern, although most fields are either rectangular or square shaped. Accordingly, a center pivot system by itself will not be able to provide water to the comers of a field, resulting in decreased production or complete loss of production therein. To increase the amount of area that can be watered by a center pivot system, high pressure sprayers known as end guns have been mounted on the end of the center pivot main arm and are actuated at the comers to produce a water spray into only a portion of the comers. Due to this fact, end guns are not an effective or efficient method for watering the comers and improved corner watering systems have been desired.
In the 1970's, the use of an additional watering arm (called a swing arm) was begun, with the swing arm being pivotally attached to the free end of the main arm to pivot out into the comers as desired. A variety of different methods for steering and driving the swing arm have been developed, but the most successful and predominantly used system for controlling the movement of the swing arm is through the use of an electromagnetically charged cable that is buried in the ground along the path that the swing arm is desired to follow. See U.S. Pat. No. 3,902,668 to Daugherty, et al.
Through the use of buried cable controls, swing arm center pivot irrigation systems have been improved in efficiency and operation. Nevertheless, there are certain drawbacks in such systems, particularly in instances where the topsoil of a field may overlie a rock substrata. In view of the fact that a buried cable system requires the laying of ten thousand or more feet of cable, when rock is present in a field, installation of the buried cable becomes unusually difficult and expensive. It is also very expensive to repair or to alter the path of the system once the cable is buried.
Other methods used to steer the swing arm include the use of encoders and angle comparisons or electrical control means with banks of switches and settings for the desired paths. See U.S. Pat. No. 4,340,183 to Kegel and U.S. Pat. No. 3,797,517 to Kircher, respectively.
Until recently the use of Global Positioning Satellite (GPS) data to guide the swing arm of a center pivot irrigation system would have been impractical from the standpoint that such position calculations were too inaccurate and GPS receiver/senders were prohibitively expensive.
The present invention is designed to provide a new and improved guidance system for the steering control of a swing arm on a center pivot system that overcomes the deficiencies of the prior art.